Green peach aphids and beet western yellows virus

We provide recent updates on confirmed BWYV virus distribution and insecticide resistance testing, along with recommendations on insecticide use and managing aphids

 

Current situation with virus and aphids

The testing program of canola samples for beet western yellows virus (BWYV) by Vic DEPI virologists has tested about 2800 plants, with overall 70% positives detected. The canola testing program is now phasing down. The latest results and information can be found mapped on the eXtension website.

Cold and wet winter conditions have reduced aphid populations and activity in many districts. Heavy frosts and/or rainfall will have caused some mortality. Aphid population growth is expected to increase when temperatures rise with the approach of spring. For the northern Mallee and all of the NSW cropping zone, maximum temperatures have been 2-4°C warmer than average since 28 July. Some winged aphids have been observed near Hopetoun in the Victorian Mallee, around Donald in the Victorian Wimmera, and near Temora in the South West Slopes district of NSW.

We recommend that growers and agronomists continue to monitor green peach aphid (GPA - Myzus persicae) populations closely. Check for the build-up of numbers and the production of significant numbers of winged aphids, which signal that flights may be about to occur. As previously advised in recent editions of PestFacts, we recommend continuing to use sticky traps to monitor for evidence of increased aphid flight activity in crops. In higher risk areas, be prepared to protect susceptible crops using appropriate insecticides. Further information on monitoring for aphids, including sourcing sticky traps, can be found in PestFacts Issue No. 7.

Update on the risk to pulse crops and control options

Although only a few positives have been detected in pulse crops for BWYV so far by Vic DEPI, pulses should be monitored for winged GPA in spring. Chickpeas, lentils, faba beans and field peas are all susceptible to BWYV, however lupins are not affected. The latest information from plant virologists is that cowpea aphids (Aphis craccivora) does not transmit BWYV. Therefore, aphid control strategies to minimise the spread of virus should focus on GPA. SARDI pathologist, Dr Jenny Davidson warns that growers and advisers should not assume that virus symptoms are caused by BWYV, as a number of viruses are found in pulses. It is important to correctly identify aphids and the virus before making a spray decision in pulses.

Insecticide resistance testing and chemical options

cesar are currently testing a number of GPA populations from various locations in south-eastern Australia for resistance to a range of insecticides. Click here to see the latest resistance testing results. All populations from Victoria and NSW tested to date have shown resistance to synthetic pyrethroid, organophosphate and carbamate insecticides. In these situations, the application of pyrethroids and/or pirimicarb will not provide control against GPA. The effectiveness of organophosphate insecticides against resistant GPA is uncertain. Some control may be achieved, however the use of organophosphates in these situations is risky and may prove ineffective (particularly if the population has been exposed to insecticides already this season which can elevate resistance levels). It is advisable to spray a test strip within the paddock to determine field efficacy of organophosphates.

Transform™ is expected to provide control of GPA for between 2 and 3 weeks. Note that as crops become well established, insecticide contact on aphids within the canopy becomes more difficult, especially as GPA are often on the underside of lower leaves. Optimal spray coverage under these conditions is critical. The manufacturer is recommending that Transform™ use should be restricted to a single application per crop per year, despite provisions on the product label for up to two applications.

It is advisable to use pirimicarb to control other canola aphids, such as cabbage aphid (Brevicoryne brassicae) and turnip aphid (Lipaphis erysimi). There is no resistance in these species and pirimicarb will conserve important aphid natural enemies such as hoverflies, lacewings, ladybird beetles and parasitic wasps.

The Australian Pesticides and Veterinary Medicines Authority (APVMA) have now approved an emergency use permit (PER14981) for the use of pirimicarb to control GPA and cowpea aphid in winter pulses, including faba bean, chickpea, lentil and field pea. Note that Transform™ insecticide is not registered in pulse crops.

 

*Sources of field reports and pest information

We thank Bill Kimber and the SARDI team (PestFacts South Australia) for compiling much of this article.

Ed Nixon - Agronomist, Landmark (NSW Central Western Slopes & Plains)

Rik Maatman - Agronomist, Landmark (Victorian Wimmera)

Kate Wilson - Consultant, AGRIvision Consultants (Victorian Mallee)